ANSWER:
-10 m/s
STEP-BY-STEP EXPLANATION:
We have the following information:
[tex]\begin{gathered} m_A=m_B=100\text{ kg} \\ v_{A1}=8\text{ m/s} \\ v_{B1}=-10\text{ m/s} \\ v_{B2}=8\text{ m/s} \end{gathered}[/tex]Now by momentum conservation equation, we have:
[tex]\begin{gathered} m_A\cdot v_{A1}+m_2\cdot v_{B1}=m_A\cdot v_{A2}+m_2\cdot v_{B2} \\ \text{replacing and solving for }v_{A2}\colon \\ 100\cdot8+100\cdot-10=100\cdot v_{A2}+100\cdot8 \\ 8-10=v_{A2}+8 \\ v_{A2}=8-10-8 \\ v_{A2}=-10 \end{gathered}[/tex]so car A will move with a velocity of -10 m/s